OBJECTIVE: The probability of bronchial asthma following bronchiolitis caused by respiratory syncytial virus (RSV) is high. This paper determined the changes of T cell subgroups in infants with bronchiolitis caused by RSV so as to investigate the association between bronchiolitis caused by RSV and asthma. METHODS: T cell subgroups were detected by flow cytometry in 21 infants with RSV bronchiolitis (Study group, mean age 10 months) and 20 age-matched healthy children (Control group). RESULTS: There were no statistical differences in the levels of CD4 and CD8 between the two groups. However, the ratio of CD4/CD8 in the Study group was significantly higher than that in the Control group (1.56±0.22 vs 1.40±0.28, P<0.05). CONCLUSIONS: The ratio of CD4/CD8 in children with bronchiolitis caused by RSV is elevated. The change of T cell subgroups is similar to that of asthma.